A variety of controllers are known for controlling switching devices, including field effect transistors (FETs). For example, control circuits are known for ORing FETs, polarity protection FETs, and synchronous rectifiers incorporated into various applications, such as power supplies.
In particular, three controllers for MOSFETs are shown in FIGS. 1-3. As shown in FIG. 1, a controller 100 is connected to control a MOSFET Q having a source terminal, a gate terminal, and a drain terminal. The controller 100 includes a bipolar junction transistor Q1 connected to the source terminal and the gate terminal of the MOSFET Q and a diode D1 connected to the drain terminal of the MOSFET Q. The control circuit 100 also includes two resistors R1, R2. As shown in FIG. 2, a controller 200 is connected to a MOSFET Q having a source terminal, a gate terminal, and a drain terminal. The controller 200 includes two bipolar junction transistors Q1, Q2 and resistors R1, R2. The transistor Q1 is connected to the source terminal of the MOSFET Q, and the transistor Q2 is connected to the drain terminal of the MOSFET Q. As shown in FIG. 3, a control circuit 300 is connected to control a MOSFET Q having a source terminal, a gate terminal, and a drain terminal. The control circuit 300 includes two bipolar junction transistors Q1, Q2. The transistor Q1 is connected to the source terminal of the MOSFET Q, and the transistor Q2 is connected to the drain terminal of the MOSFET Q. The orientation of the transistor Q2 in FIG. 3 is different than the orientation of the transistor Q2 in FIG. 2. The control circuit 300 also includes two resistors R1, R2. Each controller allows current to pass in one direction, while blocking current in a second direction.
While the control circuits discussed above are suitable for their intended purpose, the present inventors have understood a need for an improved control circuit for switching devices.